The present invention pertains generally to high-temperature resins along with their precursors and in particular to dicyanophenoxy alkanes and the cyano-addition resins prepared therefore.
Fiber-reinforced composite materials are gaining greater acceptance as a metal substitute in structural applications because of weight savings, cost effectiveness and better properties, e.g. rust resistant. New design concepts are made possible by these easily fabricated, fiber-reinforced composites with superior stiffness and a high strength-to-weight ratio. The most significant advantage of these materials is the fuel savings for moving structures manufactured from these light-weight materials.
Fiber-reinforced composite materials comprise carbon or graphite fibers dispersed in a resin. Presently, the most widely used resins are epoxies and aromatic polyimides which have several disadvantages. Conventional epoxy-based composites are limited to a maximum service temperature of 120.degree. C.; other problems associated with these composites include their brittleness, water absorptivity, and engineering reliability. While aromatic polyimides have a greater thermal stability than epoxy resins, their use has not been as extensive as epoxy resins because of their insolubility in organic solvents needed in synthesis, their poor reproducability on account of the release of water which often splits polymeric chains, trapped solvents in the final resin, and excessive stiffness.
Recently, a new class of resins has been obtained by polymerizing certain phthalonitrile terminated diamides, often referred to as amide-bridged bisorthodinitriles. The structure of these resins has not been completely confirmed, but for the following reasons, the principal mechanism of formation is theorized to be phthalocyanine nucleation. As the bisorthodinitriles polymerize, the color becomes progressively darker green in the manner similar to phthalocyanines. The polymerization is difficult to initiate and promote which indicates the formation of a large and complex nucleus such as the phthalocyanine nucleus by a large end group such as the phthalonitrile group. Examples of resins prepared from these bisorthodinitrile are disclosed in U.S. Pat. Nos. 4,056,560, 4,057,569, and 4,136,107 by James R. Griffith and Jacques G. O'Rear.
These resins with comparable structural strength have several advantages over epoxies and polyimides as structural materials. Their maximum service temperature stability in an oxygen-containing atmosphere is about 230.degree. C., a temperature being over 100.degree. C. greater than that for epoxies. Water absorptivity as measured by the water-soak method is much lower than that for epoxies. Some of the resins, depending on the bridging chain, have a much greater elastic modulus than epoxy and polyimides resins. These resins have many other advantages over polyimides due to an absence of solvents in their preparation, lower water absorptivity and not being thermoplastic with a low glass-transition temperature.
Many applications require a structural composite to have an elastic modulus high enough to withstand numerous mechanical stresses and strains over a long period of time. One application is the underbody of jet aircraft exposed to the back blast of jet engines, especially the V-STOL (vertical/standing take-off and landing) aircraft. Structural components of helicopters and automobile frames are also exposed to severe mechanical demands.